Radiation imaging apparatus and its driving method and program

ABSTRACT

As a radiation imaging apparatus which can easily and effectively correct line noise, there is provided a radiation imaging apparatus having: a conversion unit having a pixel region in which a plurality of pixels each having a conversion element ( 202 ) for converting radiation into an electric charge and a switching element ( 201 ) for outputting an electric signal based on the electric charge are arranged in a matrix; a capacitor element ( 301 ) arranged outside the pixel region; a reading out circuit unit ( 108 ) for reading out the electric signals from the pixels row by row and reading out, in parallel, a signal from the capacitor element and the electric signal from the pixel; and a correction unit for correcting the electric signal based on the signal from the capacitor element.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/271,958,filed Nov. 17, 2008, claims benefit of the filing date of thatapplication under 35 U.S.C. § 120, and claims benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2007-312825, filed Dec. 3, 2007;the entire contents of both mentioned prior applications are herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation imaging apparatus and itsdriving method and program.

2. Description of the Related Art

In recent years, a digital radiation imaging apparatus using a sensorarray in which conversion elements such as photoelectric conversionelements each for converting light into an electric signal have beenformed on an insulating substrate such as glass has been put intopractical use and has become widespread owing to the development ofsemiconductor technology.

The sensor array (conversion unit) which is used in the radiationimaging apparatus has a pixel region in which a plurality of pixels eachhaving a conversion element for converting radiation such as incidentX-rays into an electric charge and a switching element for outputting anelectric signal based on the converted electric charge are arranged in amatrix. As a conversion element, for example, an element using awavelength converter for converting radiation into light and aphotoelectric conversion element for converting the light into anelectric charge or an element for directly converting the radiation intothe electric charge is used. As a switching element, a thin filmtransistor (hereinbelow, referred to as a TFT) using amorphous siliconor polysilicon, a diode, or the like is used. A bias wiring for applyinga bias for setting the conversion element into a state where it canconvert the radiation or light into the electric charge is connected incommon to the conversion elements of a plurality of pixels. The electricsignals of the pixels are output row by row because a driving signal issupplied from a driving circuit unit to a driving wiring connected incommon to the switching elements of a plurality of pixels arranged alonga row and the switching elements are enabled row by row. A shiftregister is desirably used for the driving circuit unit and sequentiallysupplies the driving signals to a plurality of driving wirings arrangedalong a column. The electric signals generated from a plurality ofpixels arranged along the row are read out in parallel to a reading outcircuit unit through a signal wiring connected in common to theswitching elements of a plurality of pixels arranged along the column.At least an operation amplifier for amplifying the read-out electricsignal and a sampling and holding circuit (hereinbelow, also referred toas an S/H circuit) for temporarily holding a signal from the operationamplifier are provided for the reading out circuit unit for everyplurality of so many signal wirings arranged along the row. Amultiplexer for converting the signals which have been read out inparallel to the S/H circuit into a serial signal and reading out theserial signal is also provided for the reading out circuit unit. Theparallel signals which have been read out of the sensor array row by roware sequentially read out and converted into a serial signal. The analogserial signal read out of the reading out circuit unit is converted intoa digital signal by an analog to digital converter (hereinbelow,referred to as an A/D converter). By reading out the analog signals rowby row from the pixels of all rows and converting them into digitalsignals, digital image data corresponding to one image (frame) can beobtained from the radiation imaging apparatus.

In the above radiation imaging apparatus, the signals are read out rowby row. Therefore, for example, there is a case where noises are mixedin when the driving circuit unit enables the switching elements row byrow or when the electric signals which have been read out in parallelfrom the sensor array are held in a plurality of S/H circuits providedfor every signal wiring. It is considered that such noises are caused byelectromagnetic noise from outside the apparatus, a fluctuation of anoperating voltage which is supplied from a power source to the sensorarray, driving circuit unit, and reading out circuit unit, a fluctuationof a reference voltage, or the like. There is a problem in that anartifact in the form of a lateral stripe (row direction) occurs in theimage data from which the above noise has been obtained (hereinbelow,such an artifact is referred to as a line noise).

The line noise is more liable to be perceived by a diagnosing personthan is a noise component which appears at random in the image data(hereinbelow, such a noise component is referred to as random noise) andis a large factor in determining picture quality.

According to U.S. Patent Application Publication No. 2004-0174953, meansfor detecting line noise by using an output of a dark portion of anX-ray image and, further, correcting is provided, thereby removing theline noise and improving picture quality.

According to U.S. Patent Application Publication No. 2006-0065845, inorder to reduce a line noise which is generated through a signal wiring,a wiring is prepared in parallel with the signal wiring and a differencebetween noise generated in the prepared wiring and noise generated inthe signal wiring is calculated and read out, thereby correcting theline noise.

SUMMARY OF THE INVENTION

However, according to the correcting process disclosed in U.S. PatentApplication Publication No. 2004-0174953, since the output of the darkportion of a sensor array is used, at the time of correction, thepicture quality is influenced by noise due to a dark current of thepixel or by fixed pattern noise due to thermal noise, a lattice defect,or the like. As a countermeasure against such an influence, a weightedmean of a plurality of lines is obtained. However, since the amount ofdark portion which is used is not constant depending on photographing,the degree to which the influence of the noise due to the dark currentof the pixel or the fixed pattern noise due to the thermal noise,lattice defect, or the like, also is not constant, and there is a riskthat the picture quality in turn will vary depending on thephotographing. Particularly, in the form having a switching element forevery pixel, since the construction of and the manufacturing process forthe switching element are complicated and variation occurs incharacteristics of the switching elements or a lattice defect or thelike occurs, there is a risk that the influence of the fixed patternnoise becomes more remarkable.

Further, if U.S. Patent Application Publication No. 2004-0174953 isused, in addition to the pixels necessary to obtain the image data,pixels for executing the photographing of the dark portion arenecessary. In order to make the correction more precise, a larger numberof pixels for executing the photographing of the dark portion isnecessary. It is, therefore, necessary to use an imaging apparatus inwhich the area of the pixel region of the sensor array is increased andminiaturization of the apparatus is obstructed.

Further, a plurality of processes such as a process for discriminating adark portion region from the image, a process for discriminating a linenoise amount of the dark portion region from the image, a process forcorrecting the line noise, and the like have to be executed at a highspeed in a manner similar to those for a motion image. In such a case, adelay time that occurs from the obtaining of the image to a display ofthe image is extended, and it becomes a factor of deterioration inworkability at the time of an operation. In order to execute thoseprocesses in a short time, a correspondingly powerful processing unit isnecessary, so that the system becomes expensive.

According to U.S. Patent Application Publication No. 2006-0065845,wirings, in which a construction of the signal wiring which becomes afactor in the generation of line noise and a construction of the wiringwhich is capacitively coupled with the signal wiring are made identical,are separately provided, thereby correcting the line noise. According tosuch a method, an aperture ratio of the conversion elements deterioratesby a degree corresponding to the wirings which have separately beenprovided, the sensitivity of the conversion elements deteriorates, andeventually, the SNR (signal to noise ratio) of the whole systemdecreases. According to the above structure, since the separatelyprovided wirings and the driving wiring cross, the wiring capacitance ofthe driving wiring increases. Therefore, a large distortion occurs inthe driving signal and it becomes difficult to execute a high-speedoperation of the sensor array such as a photographing of a motion image.There is a risk that the enabling time of the switching element of apixel near the driving circuit unit and that of the switching element ofa pixel far from the driving circuit unit can each change, so that thereis a risk that an offset in the row direction occurs in the imageobtained.

It is an object of the invention to solve the foregoing problems and toprovide a radiation imaging apparatus which can execute high-speeddriving operation without a deterioration in picture quality and caneasily correct line noise, and to provide a driving method and a programfor such an apparatus.

According to the invention, there is provided a radiation imagingapparatus comprising: a conversion unit having a pixel region in which aplurality of pixels each having a conversion element for converting aradiation into an electric charge and a switching element for outputtingan electric signal based on the electric charge are arranged in amatrix; a capacitor element arranged outside of the pixel region; areading out circuit unit for reading out the electric signals from thepixels row by row and reading out, in parallel, a signal from thecapacitor element and the electric signal from the pixel; and acorrection unit for correcting the electric signal based on the signalfrom the capacitor element.

According to the invention, there is provided a controlling method of aradiation imaging apparatus comprising: a conversion unit having a pixelregion in which a plurality of pixels each having a conversion elementfor converting a radiation into an electric charge and a switchingelement for outputting an electric signal based on the electric chargeare arranged in a matrix; a capacitor element arranged outside of thepixel region; and a reading out circuit unit for reading out theelectric signals from the pixels row by row, wherein the methodcomprises steps of: reading out by the reading out circuit unit, inparallel, a signal from the capacitor element and the electric signalfrom the pixel; and correcting the electric signal based on the signalfrom the capacitor element.

According to the invention, there is provided a recording medium of areadable program for operating a computer to execute a controllingmethod of a radiation imaging apparatus comprising: a conversion unithaving a pixel region in which a plurality of pixels each having aconversion element for converting a radiation into an electric chargeand a switching element for outputting an electric signal based on theelectric charge are arranged in a matrix; a capacitor element arrangedoutside of the pixel region; and a reading out circuit unit for readingout the electric signals from the pixels row by row, wherein the programoperates the computer to execute steps of: reading out by the readingout circuit unit, in parallel, a signal from the capacitor element andthe electric signal from the pixel; and correcting the electric signalbased on the signal from the capacitor element.

Since the signal from the capacitor element has a line noise component,by correcting the electric signal based on the signal from the capacitorelement obtained in parallel with the signal from the pixel, the linenoise in the image can be easily and properly removed. Since thecapacitor element arranged outside of the pixel region is used,different from the case of using a dark portion output of the pixel, theinfluence of noise due to a dark current of the pixel or a fixed patternnoise due to thermal noise, a lattice defect, or the like can beprevented.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic equivalent circuit diagram of a radiation imagingapparatus in the first embodiment of the invention.

FIG. 2 is a timing chart for driving a sensor array which is used in theradiation imaging apparatus of the invention and obtaining a radiationimage.

FIG. 3 is a conceptual diagram illustrating a correcting method of aline noise in the first embodiment of the invention.

FIG. 4 is a schematic equivalent circuit diagram of another radiationimaging apparatus in the first embodiment of the invention.

FIG. 5 is a schematic equivalent circuit diagram of still anotherradiation imaging apparatus in the first embodiment of the invention.

FIGS. 6A and 6B are schematic cross-sectional views of a pixel using aphotoelectric conversion element which is desirably used for aconversion element of the radiation imaging apparatus of the invention.

FIG. 7 is a schematic constructional diagram of a radiation imagingsystem using the radiation imaging apparatus of the invention.

FIG. 8 is a schematic equivalent circuit diagram of a radiation imagingapparatus in the second embodiment of the invention.

FIG. 9 is a conceptual diagram illustrating a correcting method for linenoise in the second embodiment of the invention.

FIG. 10 is a schematic equivalent circuit diagram of a radiation imagingapparatus in the third embodiment of the invention.

FIG. 11 is a conceptual diagram illustrating a correcting method forline noise in the third embodiment of the invention.

FIG. 12 is a schematic diagram typically illustrating a structure of theradiation imaging apparatus in the third embodiment of the invention.

FIG. 13 is a conceptual diagram for describing a correcting method usinga radiation imaging apparatus in the fourth embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

First, a radiation imaging system using a radiation imaging apparatus ofthe invention will be described with reference to FIG. 7. FIG. 7 is aschematic constructional diagram of the radiation imaging system usingthe radiation imaging apparatus of the invention. In the invention, itis assumed that besides beams of α-particles, β-particles, and γ-rays,and the like as beams which are formed by particles (including photons),which are radiated by a radiation decay, beams having energies of levelswhich are equal to or larger than those of such beams, for example, anX-ray beam, corpuscular rays, cosmic rays, and the like are alsoincluded within the term “radiation”. In the embodiment, a descriptionwill be made by using an X-ray imaging apparatus using X-rays as theincident radiation.

A construction of a typical digital radiation imaging system isillustrated in FIG. 7. A part of the X-ray beam radiated from an X-raysource 101 is absorbed by an object (object to be photographed) 113. TheX-rays that have been transmitted through the object 113 arrive at andirradiate an X-ray imaging apparatus 111. The X-ray imaging apparatus111 converts the received X-rays into an electric signal by a sensorarray 110, is driven by a driving circuit unit 112, and outputs theelectric signal to a reading out circuit unit 108 row by row. Theelectric signal input to the reading out circuit unit 108 is amplifiedby an operation amplifier provided in the reading out circuit unit 108and, thereafter, converted into a digital signal by an A/D converterprovided in a system circuit unit 107. The converted digital signal istransmitted to a processing circuit unit 106 from the system circuitunit 107. The transmitted digital signal is image processed by one ofthe processing circuit unit 106 and a control PC 103. The imageprocessed digital signal is used to display the image onto a monitor 105or stored into a memory. The control PC 103 transmits control signals tothe processing circuit unit 106 in order to control the reading outcircuit unit 108, driving circuit unit 112, and sensor array 110provided in the X-ray imaging apparatus 111. The processing circuit unit106 controls the system circuit unit 107, reading out circuit unit 108,and driving circuit unit 112 based on the control signals. Operatingvoltages and a reference voltage are supplied from a power source unit109 to the sensor array 110, driving circuit unit 112, reading outcircuit unit 108, and the system circuit unit 107 provided in the X-rayimaging apparatus 111 through the control PC 103 and the processingcircuit unit 106, respectively. The control PC 103 also controls theirradiation of the X-rays from the X-ray source through an X-ray controlapparatus 102. Various kinds of information are input to the control PC103 from a control panel 104. The control PC 103 makes various kinds ofcontrol based on the input information.

Subsequently, a circuit construction of the radiation imaging apparatusin the first embodiment of the invention will be described withreference to FIG. 1. FIG. 1 is a schematic equivalent circuit diagram ofthe radiation imaging apparatus of the embodiment and corresponds to theX-ray imaging apparatus 111 in FIG. 7.

The sensor array has a pixel region 211 in which a plurality of pixelseach having a conversion element 202 for converting the radiation intoan electric charge and a switching element 201 for outputting anelectric signal based on the converted electric charge are arranged in amatrix. In the embodiment, a wavelength converter for converting theradiation into light and a photoelectric conversion element forconverting the light into an electric charge are used as a conversionelement 202. A TFT of amorphous silicon is used as a switching element201. Driving wirings Vg1 to Vg3 are connected in common to the switchingelements of a plurality of pixels arranged along a row and a pluralityof driving wirings are arranged along a column. Signal wirings Sig1 toSig3 are connected in common to the switching elements of a plurality ofpixels arranged along the column and a plurality of signal wirings arearranged along the row. A bias wiring for applying a bias adapted toenable the conversion element 202 to convert the radiation or light intothe electric charge is connected in common to the conversion element 202of each pixel. The sensor array (conversion unit) is constructed byhaving those component elements. In the sensor array, the switchingelements 201 and conversion elements 202 are formed on an insulatingsubstrate such as glass or the like by using an amorphous siliconprocess.

The driving circuit unit 112 for outputting driving signals havingenabling voltages for enabling the switching elements 201 to theswitching elements 201 is connected to the driving wirings Vg1 to Vg3,respectively. The driving circuit unit 112 outputs the driving signalsformed by input voltage (enabling voltage and disabling voltage) valuesfrom two power sources according to pulses (DCLK, OE, DIO) which havebeen input. The driving circuit unit 112 sequentially supplies thedriving signals to a plurality of driving wirings Vg1 to Vg3 arrangedalong the column, thereby allowing the switching elements 201 to outputthe electric signals from the pixels to the signal wirings Sig1 to Sig3row by row. The reading out circuit unit 108 for reading out theelectric signals from the pixels in parallel row by row is connected tothe signal wirings Sig1 to Sig3. A sensor power source 203 for applyinga bias (Vs) for enabling the conversion element 202 to convert theradiation or light into the electric charge is electrically connected tothe bias wiring. As for the sensor power source 203, a magnitude and apolarity of a voltage value which is used, the number of power sources,and the like differ depending on a structure of the conversion element202 and a converting method and the conversion elements 202 are properlyselected so that a sufficient S/N ratio can be obtained.

In the reading out circuit unit 108, an operation amplifier 205 of anintegrating type is electrically connected to each signal wiring in aone-to-one correspondence relational manner. In the operation amplifier205 of the integrating type, its amplification factor can be changed bychanging the number of capacitors connected to a feedback unit of theamplifier and their capacitances. A reference power source (VREF) 206 iselectrically connected to the operation amplifier 205 and a referencevoltage is supplied thereto from the reference power source. Theoperation amplifier 205 outputs a voltage which is proportional to anelectric charge amount integrated by using the reference voltage as areference. Further, a variable gain amplifier unit 204 havingamplifiers, each of which amplifies the signal from the operationamplifier 205 and whose amplification factor can be changed, providedfor each of the signal wirings Sig1 to Sig3, is connected at a stagefollowing to the operation amplifier 205 of the integrating type. Asampling and holding circuit unit 207 in which sampling and holdingcircuits (hereinbelow, also referred to as S/H circuits) for temporarilyholding the output signals are provided for each of the signal wiringsSig1 to Sig3 is connected at a stage following to the variable gainamplifier unit 204.

The amplifiers which are used in the variable gain amplifier unit 204have substantially the same circuit construction as that of theoperation amplifier 205, and their amplification factors can be changedby changing the number of capacitors and their capacitances in a mannersimilar to that in the operation amplifier 205 Further, correlateddouble sampling is executed by shifting reset timing for the operationamplifier 205 and reset timing for the variable gain amplifier unit 204and the noise which is caused in the operation amplifier 205 can becancelled. Although not shown, the S/H circuit unit 207 has a set of atransfer switch and a holding capacitor for each of the signal wiringsSig1 to Sig3. By collecting a plurality of sets, the S/H circuit unit207 is constructed.

One set including the operation amplifier 205, the amplifier of thevariable gain amplifier unit 204, and the transfer switch and theholding capacitor of the S/H circuit unit 207 is provided incorrespondence to one signal wiring. In the specification, one setincluding the operation amplifier 205, the amplifier of the variablegain amplifier unit 204, and the transfer switch and the holdingcapacitor of the S/H circuit unit 207 which are connected to the signalwiring is called a channel (first reading out circuit). The operationamplifier 205 provided for the channel for reading out the signal fromthe sensor array is called a first operation amplifier. A multiplexer208 for converting the signals which have been read out of the pixels inparallel row by row through a plurality of channels into a serial signaland reading out the serial signal is provided for the reading outcircuit unit 108. By such a construction, the reading out circuit unit108 sequentially converts the parallel signals read out of the sensorarray row by row into the serial signal.

In the embodiment, separately from the channel for reading out thesignals from the pixel region 211 of the sensor array in which aplurality of pixels are arranged in a matrix, a correction channel(second reading out circuit) is provided in order to read out a signalfor correcting the line noise. A capacitor element (correction element)301 which is provided outside of the pixel region (external region ofthe pixel region 211) and is used to obtain the signal for correctingthe line noise is connected to the correction channel.

Although not illustrated in FIG. 1, the capacitor element 301 forcorrecting the line noise may be formed on an insulating substrate suchas a glass substrate or the like and outside of the pixel region 211 ofthe sensor array. In this instance, the capacitor element 301 may beformed on the switching element 201 from the same layer as that ofamorphous silicon nitride film which is used as an insulating layer orfrom the same layer as that of aluminum or the like which is used as anelectrode. The capacitor element 301 may be formed from the same layeras the layer which is used for the conversion element 202. The capacitorelement 301 may be formed in a crystalline semiconductor chipconstructing the reading out circuit unit 108 from the same layer as asilicon oxide film which is used as an insulating layer in anotheroperation amplifier 205, the holding capacitor of the S/H circuit unit207, or the like or from the same layer of aluminum or the like which isused a wiring.

As illustrated in FIG. 1, one electrode of the capacitor element 301 iselectrically connected to an input of the operation amplifier 205 whichis used for the correction channel. The other electrode of the capacitorelement 301 is electrically connected to a reference power source forapplying a reference voltage (grounding potential) to the operationamplifier 205. In the specification, the operation amplifier 205 whichis used for the correction channel is called a second operationamplifier.

By such a construction, a fluctuation in the reference power source 206for applying the reference voltage to the operation amplifier 205 and afluctuation in the reference potential (grounding potential) which areone of the main factors of the line noise are detected by the capacitorelement 301 for correcting the line noise. The reference voltage isinput to the operation amplifier 205 of the correction channel connectedto the capacitor element 301 and is simultaneously read out when theother channel reads out the electric signal from the sensor array, sothat the fluctuations in the reference power source and referencepotential which become the main factor of the line noise are obtained.

The fluctuations in the reference power source 206 and reference voltageare amplified by a ratio (that is, Ccor/Cf) between a capacitance Ccorof the capacitor element 301 and a feedback capacitance Cf of theoperation amplifier 205 of the correction channel. Therefore, it isdesirable that the capacitance value of the capacitor element 301 forcorrecting the line noise is set to a value which is equal to or largerthan a parasitic capacitance of the signal wirings Sig1 to Sig3 of thesensor array.

The voltage which is applied to the other electrode of the capacitorelement 301 is not limited to the voltage which is supplied from thereference power source 206 connected to the operation amplifier 205mentioned above. For example, the other electrode of the capacitorelement 301 may be connected to the sensor power source 203 asillustrated in FIG. 4. The sensor power source 203 is capacitivelycoupled with the signal wirings Sig1 to Sig3 through the pixels. Throughthe signal wirings Sig1 to Sig3, the fluctuation in the sensor powersource 203 is input to all channels connected to the sensor arraythrough the signal wirings Sig1 to Sig3. Therefore, a fluctuation in thebias which is supplied from the sensor power source 203 also causes theline noise. By connecting the input of the operation amplifier 205 ofthe correction channel to the sensor power source 203 through thecapacitor element 301 as illustrated in FIG. 4, the fluctuation in thebias which is supplied from the sensor power source 203 can be fetchedsimultaneously with the fetching of the image. It is desirable that thecapacitance value of the capacitor element 301 in FIG. 4 is set to avalue which is equal to or larger than a capacitance coupling amount ofthe signal wirings Sig1 to Sig3 and the bias wiring.

Although FIG. 5 illustrates a construction in which a sensor powersource 602 is connected to the other electrode of the capacitor element301 in a manner similar to FIG. 4, it differs from FIG. 4 with respectto a point that the sensor power source is constructed by a plurality ofsensor power sources 601 and 602. In the case of such a constructionusing the sensor power sources, it is desirable that the sensor powersource 602 for supplying a voltage to the conversion element 202 at thetime of the accumulating operation, which will be described hereinafter,is connected to the other electrode of the capacitor element 301.

The multiplexer 208 for time-sequentially reading out the electricsignals accumulated in a holding capacitor of the S/H circuit unit 207is provided at a stage following to the S/H circuit unit 207. An analogserial signal read out of the multiplexer 208 is sequentiallytransferred to an A/D converter 210 through a buffer amplifier 209.

The A/D converter 210 converts the analog signal which is output fromthe buffer amplifier 209 into a digital signal. The digital signaloutput from the A/D converter 210 is stored as image data into a framememory 212. In this manner, the digital image data corresponding to oneimage (frame) can be obtained from the radiation imaging apparatus.

An indirect type conversion element in which a photoelectric conversionelement for converting light in a wavelength band which can be perceivedinto an electric charge and a wavelength converter for convertingradiation into light in a wavelength band which can be perceived by thephotoelectric conversion element are combined is used as a conversionelement 202 of the embodiment. However, the invention is not limited tosuch an indirect type conversion element, but a direct type conversionelement for directly converting a radiation into an electric charge maybe used. As an indirect type conversion element, an MIS(Metal-Insulator-Semiconductor) type photoelectric conversion element ora PIN type photoelectric conversion element is desirably used. As adirect type conversion element, a material containing any one ofamorphous selenium, GaAs, HgI₂, PbI₂, CdTe, and ZnS as a main componentis used.

FIG. 6A illustrates a schematic cross sectional view of a pixel usingthe MIS type photoelectric conversion element which is desirably usedfor the conversion element of the radiation imaging apparatus of theinvention. As illustrated in FIG. 6A, a TFT which is used as a switchingelement 201 is formed on an insulating substrate 801 such as a glasssubstrate. A driving wiring and a gate electrode 820 are formed by usingaluminum or an alloy containing aluminum. A gate insulating film 802 isformed by an amorphous silicon nitride film. A semiconductor layer 803serving as a channel of the TFT is made of amorphous silicon hydride(a-Si:H). An impurity semiconductor layer 804 is made of amorphoussilicon in which N type impurities have been doped and is a layer formaking an ohmic contact between the semiconductor layer 803 and a sourceelectrode layer 805/drain electrode layer 806, which will be describedhereinafter. The source electrode layer 805 and the drain electrodelayer 806 are formed from the same conductive layer and made of a metalsuch as aluminum or an alloy of aluminum.

A lower electrode (first electrode) 807 of an MIS type photoelectricconversion element 816 is made of a metal such as chromium, aluminum, oran alloy of aluminum or the like formed on the insulating substrate 801.An insulating layer 808 serving as an insulating layer of the MIS typephotoelectric conversion element 816 is made of an amorphous siliconnitride film. A semiconductor layer 809 serving as a photoelectricconversion element for converting visible light into an electric signalis made of amorphous silicon hydride. An impurity semiconductor layer810 is made of amorphous silicon in which N type impurities have beendoped and is a layer for making an ohmic contact between thesemiconductor layer 809 and an upper electrode 811, which will bedescribed hereinafter. The impurity semiconductor layer 810 has afunction for blocking that holes are doped from a bias wiring 818. Theupper electrode (second electrode) 811 is used to supply a bias to theMIS type photoelectric conversion element 816 and is formed by atransparent conductive layer made of ITO or the like. The bias wiring818 is made of a metal material such as aluminum or chromium which isused as a well-known wiring material.

A protecting layer 812 is a layer to protect the photoelectricconversion element 816 and the TFT 201 against moisture in the open airor a foreign matter from phosphor 814 and is formed by an inorganicinsulating layer such as silicon nitride film or silicon oxide film. Amoisture barrier layer 813 is a layer to protect the phosphor 814 andthe sensor array against the moisture in the open air and is formed byan inorganic insulating layer such as silicon nitride film or siliconoxide film or by an organic insulating layer such as polyimide. Asphosphor 814 as a wavelength converter for converting a radiation intovisible light, for example, a material of a gadolinium system such asGd₂O₂S or Gd₂O₃ or a material such as CsI (cesium iodide) is used. Aphosphor protecting layer 815 is a layer to protect the phosphor 814against the moisture in the open air or a shock from the outside.

FIG. 6B illustrates a schematic cross-sectional view of a pixel usingthe PIN type photoelectric conversion element which is desirably usedfor the conversion element of the radiation imaging apparatus of theinvention. The TFT which is used as a switching element 201 is formed onan insulating substrate 901 such as a glass substrate. A driving wiringand a gate electrode 902 are formed by using aluminum or an alloycontaining aluminum. A gate insulating film 903 is formed by anamorphous silicon nitride film. A semiconductor layer 904 serving as achannel of the TFT is made of amorphous silicon hydride (a-Si:H). Animpurity semiconductor layer 905 is made of amorphous silicon in which Ntype impurities have been doped and is a layer for making an ohmiccontact between the semiconductor layer 904 and a source electrode layer906 and a drain electrode layer 907, which will be describedhereinafter. The source electrode layer 906 and the drain electrodelayer 907 are formed from the same conductive layer and made of a metalsuch as aluminum or an alloy containing aluminum.

A lower electrode (first electrode) 909 of a PIN type photoelectricconversion element 919 is made of a metal such as aluminum or an alloycontaining aluminum formed on the insulating substrate 901. A firstimpurity semiconductor layer 910 is made of amorphous silicon in whichN-type (first conductivity type) impurities have been doped and is alayer to prevent holes from being doped into a semiconductor layer 911from the lower electrode 909. The semiconductor layer 911 serving as aphotoelectric conversion layer for converting the visible light into anelectric signal is made of amorphous silicon hydride. A second impuritysemiconductor layer 912 is made of amorphous silicon in which impuritiesof a P-type (second conductivity type) as a conductivity type oppositeto the N-type (first conductivity type) have been doped. The secondimpurity semiconductor layer 912 has a function for making an ohmiccontact between the semiconductor layer 911 and an upper electrode 913and blocking that electrons are doped from a bias wiring 914. The upperelectrode (second electrode) 913 is used to supply a bias to the PINtype photoelectric conversion element 919 and is formed by a transparentconductive layer made of ITO or the like. The bias wiring 914 is made ofa metal material such as aluminum or chromium which is used as awell-known wiring material.

A protecting layer 915 is a layer to protect the photoelectricconversion element 919 and the TFT 201 against the moisture in the openair or a foreign matter from phosphor 917 and is formed by an inorganicinsulating layer such as silicon nitride film or silicon oxide film. Amoisture barrier layer 916 is a layer to protect the phosphor 917 andthe sensor array against the moisture in the open air and is formed byan inorganic insulating layer such as silicon nitride film or siliconoxide film or by an organic insulating layer such as polyimide. As amaterial of the phosphor 917 as a wavelength converter for convertingradiation into visible light, for example, a material of a gadoliniumsystem or a material such as CsI (cesium iodide) is used. A phosphorprotecting layer 918 is a layer to protect the phosphor 917 against themoisture in the open air or a shock from the outside.

As already mentioned before, the capacitor element 301 may be formed onthe insulating substrate simultaneously with the photoelectricconversion element 202 and TFT 201. In this instance, it is desirablethat the capacitor element 301 is formed simultaneously with the timingwhen the gate insulating films, gate electrodes, and signal wiringsillustrated in FIGS. 6A and 6B are formed and the layer constructionsand the film thicknesses are also similarly set. The invention is notlimited to such a construction but the capacitor element 301 may beformed in a crystalline semiconductor IC constructing the reading outcircuit unit 108 from the same layer as that of the silicon oxide filmwhich is used as an insulating layer in the operation amplifier 205, theholding capacitor of the S/H circuit unit 207, or the like or from thesame layer as that of aluminum or the like which is used as a wiring.

Subsequently, a driving method for obtaining a radiation image by usingthe radiation imaging apparatus of the invention will be described withreference to FIG. 2. FIG. 2 shows a timing chart for driving the sensorarray which is used in the radiation imaging apparatus of the inventionand obtaining the radiation image. When a signal X-RAY is set to thehigh level, the X-ray source 101 (FIG. 7) irradiates an X-ray beam. Asignal RC is a control signal for resetting a feedback capacitor of theoperation amplifier 205 and the signal wiring and is input to a resetswitch of the operation amplifier 205. A signal DRC is a control signalwhich is input to the variable gain amplifier unit 204. A signal MUX isa control signal which is input to the multiplexer 208 and is used tospecify operation timing for the multiplexer. Signals DCLK, CIO, and OEare control signals which are input to the driving circuit unit 112 andare used to specify operation timing for the driving circuit unit 112. Asignal SH is a control signal which is input to the S/H circuit unit 207and is used to specify sampling and holding timing. Those controlsignals are supplied from the processing circuit unit 106 or the systemcircuit unit 107 in FIG. 7. A signal Vout is an output signal from thebuffer amplifier 209 in FIG. 1.

First, the bias (Vs) necessary for the conversion element 202 issupplied from the sensor power source 203 and the switching element 201is disabled. Such an operation of the sensor array is called anaccumulating operation Wait. By irradiating the X-rays by means of thesignal X-RAY while the sensor array is executing the accumulatingoperation Wait, the electric charges based on information of the X-rayswhich have transited through the object are accumulated in theconversion element 202.

Subsequently, the electric signal based on the electric chargesaccumulated in the conversion element 202 is input to the reading outcircuit unit 108. Such a reading operation is called “Read”. In thereading operation Read-row1 of the first row, first, the control signalsRC and DRC are set to Hi (high level) and an input and an output of theoperation amplifier 205 and variable gain amplifier unit 204 of eachchannel are short-circuited, thereby resetting the operation amplifier205 and the variable gain amplifier unit 204. By executing the resettingoperation prior to outputting the signal from the conversion element202, the unnecessary signals which have been input to the operationamplifier 205 and variable gain amplifier unit 204 are erased during theaccumulating operation, so that the picture quality is improved.

At this time, the control signals DCLK and DIO are input to the drivingcircuit unit 112, thereby enabling Vcom (enabling voltage) as a voltagefor enabling the switching elements 201 to be supplied to the drivingwirings Vg1 to Vg3 simultaneously with that the control signal OE is setto Hi (high level). The control signal RC is set to Lo (low level) andthe resetting of the operation amplifier 205 is finished. Subsequently,after the lapse of a proper time, the signal DRC is switched from Hi toLo and the resetting of the variable gain amplifier unit 204 isfinished.

Subsequently, the control signal OE is set to Hi in order to enable theswitching element 201 of the first row (row1). Simultaneously with thatthe control signal OE is set to Hi, the voltage of the driving wiringVg1 of the first row (row1) is switched from Vss (disabling voltage) toVcom (enabling voltage) and switching elements T11 to T13 of the firstrow are enabled. Thus, electric signals based on the electric chargesaccumulated in conversion elements S11 to S13 of the pixels of the firstrow are output to the operation amplifiers 205 through the switchingelements T11 to T13 and the signal wirings Sig1 to Sig3. At this time,an electric signal based on the electric charge accumulated in thecapacitor element 301 is also read out by the operation amplifier 205 ofthe correction channel of the reading out circuit unit 108 for the sameperiod of time as that during which the electric signals of the pixelsare output. In other words, the electric signal based on the electriccharge in the capacitor element 301 is output in parallel with theelectric signals from the pixels and derived by the operation amplifier205 of the correction channel of the reading out circuit unit 108.

After the switching elements T11 to T13 were enabled for a time enoughto transfer the electric signals based on the electric chargesaccumulated in the conversion elements S11 to S13, the signal OE is setto Lo and the switching elements T11 to T13 are disabled. At a point oftime when the switching elements T11 to T13 are disabled, the electricsignals (voltages) according to the electric charges accumulated in theconversion elements S11 to S13 are output as output signals of thevariable gain amplifier unit 204.

After the elapse of a proper time after the switching elements T11 toT13 of the first row had been disabled, the control signal SH is set toHi, thereby allowing the output of the variable gain amplifier unit 204of each channel to be sampled and held in the holding capacitor of eachchannel in the S/H circuit unit 207. After the sampling and holdingoperations have been finished by setting the control signal SH to Lo, areading operation Read-row2 of the second row (row2) is similarlyexecuted.

At this time, the control signal MUX is input to the multiplexer 208 inparallel with the resetting of the operation amplifier 205 in thereading operation of the second row or the switching of theenabling/disabling operations of switching elements T21 to T23. Thus,the signals held in the holding capacitor in the S/H circuit unit 207 ofeach channel are time-sequentially read out, and a serial signal isoutput. The analog serial signal output from the multiplexer 208 is sentto the A/D converter 210 through the buffer amplifier 209. The A/Dconverter 210 converts the analog serial signal into a digital signaland transmits the digital signal to the frame memory 212.

In the reading operation Read-row2 of the second row, by controlling thedriving wiring Vg2 in a manner similar to the reading operation of thefirst row, the switching elements T21 to T23 are enabled. Thus, electricsignals based on the electric charges accumulated in conversion elementsS21 to S23 are output to the operation amplifiers 205 through theswitching elements T21 to T23 and the signal wirings Sig1 to Sig3. Atthis time, in a manner similar to the reading operation of the firstrow, the electric signal based on the electric charge in the capacitorelement 301 is also read out by the operation amplifier 205 of thecorrection channel of the reading out circuit unit 108 for the sameperiod of time as that during which the electric signals of the pixelsare output. Further, after the signals of the pixels of the second rowwere sampled and held, a reading operation Read-row3 of the third row issimilarly executed. In the reading operation Read-row3, by controllingthe driving wiring Vg3 in a manner similar to the reading operation ofthe first or second row, switching elements T31 to T33 are enabled.Thus, electric signals based on the electric charges in conversionelements S31 to S33 are output to the operation amplifiers 205 throughthe switching elements T31 to T33 and the signal wirings Sig1 to Sig3.At this time, in a manner similar to the reading operation of the firstor second row, the electric signal based on the electric charge in thecapacitor element 301 is also read out by the operation amplifier 205 ofthe correction channel of the reading out circuit unit 108 for the sameperiod of time as that during which the electric signals of the pixelsare output. In this manner, in order to read out the electric signalsfrom the pixels of the second and third rows, it is sufficient toexecute the operations within a range from the control signal RC=Hi tothe control signal SH=Lo. As illustrated in FIG. 2, by repetitivelyexecuting the reading operation with respect to the three rows, the dataof one X-ray image and the correction data can be obtained. In thismanner, the correction channel to which the capacitor element 301 isconnected reads out the electric signal from the capacitor element 301during substantially the same reading operation as that of the channelto which the signal wirings Sig1 to Sig3 are connected. Thus, theelectric signal corresponding to the line noise component which isgenerated for a period of time from the end of the resetting of theoperation amplifier 205 to the end of the sampling and holdingoperations can be sampled and held into the holding capacitor of thecorrection channel of the S/H circuit unit 207. The sampled and heldelectric signal corresponding to the line noise component is output bythe multiplexer in a manner similar to the electric signal from thechannel connected to the sensor array. After that, output electricsignal is converted into a digital signal by the A/D converter 210 andthe digital signal is stored into the frame memory 212, so that the datafor correction can be obtained within the same period as that of thedata of one X-ray image.

Now, a correcting method of the line noise in the embodiment will bedescribed with reference to FIG. 3. FIG. 3 is a conceptual diagramillustrating the correcting method of the line noise in the firstembodiment of the invention. In FIG. 3, the X-ray image data obtained bythe driving method already mentioned above is schematically illustratedin the frame memory 212. Information from the pixel of the first rowrow1 and the first column col1 (T11 and S11 in FIG. 1) is illustrated asI(1, 1).

As illustrated in FIG. 3, the fetched data is constructed by: data I(1,1) to I(3, 3) of 3×3 X-ray images constructing the X-ray imageinformation; and correction data I(1, 4) to I(3, 4) for correcting theline noise which has been output from the capacitor element 301.

The correction data I(1, 4) to I(3, 4) is data based on the signalswhich were obtained within the same period of time when the X-ray imagesare obtained and which were output from the correction channels to whichthe capacitor element 301 is connected. Therefore, the correction dataI(1, 4) to I(3, 4) does not include the signal components correspondingto the image signal but signal components which are caused by thereference voltage that is supplied from the reference power source 206and becomes a cause of the line noise or by a fluctuation such as asensor bias which is supplied from the sensor power source 203 arecontained. Assuming that a capacitance ratio p is equal to 1, acorrection unit 501 for executing a correcting process of the line noisesubtracts the X-ray image data I(m, n) in the frame memory 212 by usingcorrection data I(m, 4) obtained in the same period of time as that ofthe X-ray image data I(m, n). By this method, the correction unit 501corrects the line noise of the X-ray image data, obtains corrected X-rayimage data I′(m, n), and writes it into the frame memory 212.

The capacitance ratio p will now be described. If the reference powersource 206 of the operation amplifier 205 is connected to the otherelectrode of the capacitor element 301 as illustrated in FIG. 1, a ratiobetween the capacitance value of the capacitor element 301 and theparasitic capacitance value of the signal wirings Sig1 to Sig3 isassumed to be p. Therefore, the corrected X-ray image data I′(m, n) isobtained by the following equation:

I′(m, n)=I(m, n)−I(m, 4)/p

where the capacitance ratio p is a natural number. That is, if thecapacitance value of the capacitor element 301 and the parasiticcapacitance value of the signal wirings Sig1 to Sig3 are equal, it issufficient to subtract the X-ray image data I(m, n) by using thecorrection data I(m, 4) obtained in the same period of time as that ofthe X-ray image data I(m, n).

If the sensor power source 203 is connected to the other electrode ofthe capacitor element 301 as illustrated in FIGS. 4 and 5, a ratiobetween the capacitance value of the capacitor element 301 and acapacitance value between the bias wiring and the signal wirings Sig1 toSig3 is assumed to be p and is obtained by the above equation. That is,if the capacitance value of the capacitor element 301 and thecapacitance value between the bias wiring and the signal wirings Sig1 toSig3 are equal, it is sufficient to subtract the X-ray image data I(m,n) by using the correction data I(m, 4) obtained in the same period oftime as that of the X-ray image data I(m, n). By such a process, thecorrection can be executed by using a component of an amount which isalmost equal to that of the line noise component which is multiplexed tothe X-ray image. After the above process was executed, the correctionunit 501 corrects the line noise by the process and writes the correctedX-ray image data I′(m, n) into the frame memory 212.

In the embodiment, the number of pixels of the sensor array is notlimited to 9 (=3×3) as a total number of pixels but the invention can bealso realized even if it is equal to a pixel pitch necessary as aradiation imaging system or the number of pixels which is calculatedfrom an imaging area. The number of capacitor elements 301 is notlimited to 1. The number of correction channels connected to thecapacitor element 301 is not limited to 1 but the system may have aplurality of correction channels. The number of driving circuit units112 is not limited to 1. The number of switching elements 201 in thepixel is not limited to 1. That is, the number of pixels in the pixelregion 211 of the sensor array, the number of reading out circuit units108, the number of channels in the reading out circuit unit 108, thenumber of driving circuit units 112, and the number of switchingelements 201 in one pixel are not limited to the numbers shown in theembodiment, respectively.

Each of the reading out circuit unit 108 and the driving circuit unit112 in the invention may be constructed by a transistor formed on amonosilicon chip by using a photolithography, sputtering method,epitaxial growing method, or the like or by a transistor formed on aninsulating substrate of an outer periphery of the pixel region 211 by apolysilicon process.

Although an example in which the processed data is stored into anotherarea in the frame memory 212 in FIG. 3 has been shown in the embodiment,a method whereby the corrected X-ray image data is overwritten to theX-ray image data before processing and the correction data I(m, 4) isfinally deleted may be used.

The power source connected to the other electrode of the capacitorelement 301 is not limited to one kind but may be a combination of thereference power source 206 of the operation amplifier 205 and the sensorbias power source 203.

The correction unit 501 in the embodiment may be one of software whichoperates in a computer for executing the image processes of theradiation imaging system and a program which has been programmed in anLSI. In such a case, one of the processing circuit unit 106 and thecontrol PC 103 in FIG. 7 executes a program stored in an internalstoring apparatus, thereby executing the correcting process of thecorrection unit 501. Means for supplying the program to the computer,for example, a computer-readable recording medium such as a CD-ROM inwhich such a program has been recorded or a transmission medium such asInternet for transmitting such a program can be also applied as anembodiment of the invention. A computer program product such as acomputer-readable recording medium in which the foregoing program hasbeen recorded can be also applied as an embodiment of the invention. Theforegoing program, recording medium, transmission medium, and computerprogram product are incorporated in the purview of the invention. As arecording medium, for example, a flexible disk, a hard disk, an opticaldisk, a magnetooptic disk, a CD-ROM, a magnetic tape, a non-volatilememory card, a ROM, or the like can be used.

Second Embodiment

A sensor array according to the second embodiment of the invention and acorrecting process using the sensor array will now be described withreference to FIGS. 8 and 9. FIG. 8 is a schematic equivalent circuitdiagram of a radiation imaging apparatus in the second embodiment of theinvention. In the embodiment, the radiation imaging apparatus in which aplurality of capacitor elements 301 and a plurality of correctionchannels connected to the capacitor elements 301 described in the firstembodiment are arranged will be described. Although an example in whichtwo capacitor elements 301 and two correction channels are arranged isillustrated in FIG. 8 for convenience of description, the number ofcapacitor elements 301 and the number of correction channels are notlimited to 2 but may be a plural number of 2 or more. Since otherdriving methods, functions, and the like are similar to those in thefirst embodiment, their detailed description is omitted here.

FIG. 9 is a conceptual diagram illustrating a correcting method of aline noise in the second embodiment of the invention. According to thecorrecting method of the second embodiment, the correction data I(m, 4)and I(m, 5) obtained from the two capacitor elements 301 and the twocorrection channels for the same period of time in correspondence to thereading operation of each row of the sensor array are averaged and,thereafter, a subtracting process with the X-ray image data I(m, n) isexecuted. That is, a line noise correction unit 1101 calculates thefollowing equation in order to obtain the corrected X-ray image dataI′(m, n):

I′(m, n)=I(m, n)−(I(m, 4)+I(m, 5))/(2×p)

In the embodiment, by using a mean value of a plurality of correctiondata I(m, 4) and I(m, 5), a contribution degree of the random noisecomponent which is generated in the capacitor elements 301 andcorrection channels connected thereto can be reduced at the time of thecorrecting process. Thus, the line noise can be corrected moreaccurately. The above random noise component includes a 1/f noise of theoperation amplifier 205 and the variable gain amplifier unit 204 of thecorrection channel and a KTC noise of the transfer switch or the likeused in the correction channel of the S/H circuit unit 207.

Also in the embodiment, in a manner similar to the first embodiment, ifthe reference power source 206 of the operation amplifier 205 isconnected to the other electrode of the capacitor element 301, the ratiobetween the capacitance value of the capacitor element 301 and theparasitic capacitance value of the signal wirings Sig1 to Sig3 isassumed to be p. If the sensor power source 203 is connected to theother electrode of the capacitor element 301, the ratio between thecapacitance value of the capacitor element 301 and the capacitance valuebetween the bias wiring and the signal wirings Sig1 to Sig3 is assumedto be p and is obtained by the above equation.

Although an example in which the processed data is stored into anotherarea in the frame memory 212 in FIG. 9 has been shown in the embodiment,the invention is not limited to such a method. A method whereby thecorrected X-ray image data is overwritten to the X-ray image data beforeprocessing and the correction data I(m, 4) and I(m, 5) are finallydeleted may be used in a manner similar to the first embodiment.

In a manner similar to the first embodiment, the correction unit 1101 inthe embodiment illustrated in FIG. 9 may be one of the software whichoperates in a computer for executing the image processes of theradiation imaging system and the program which has been programmed inthe LSI.

Third Embodiment

A sensor array according to the third embodiment of the invention and acorrecting process using the sensor array will now be described withreference to FIGS. 10 and 11. FIG. 10 is a schematic equivalent circuitdiagram of a radiation imaging apparatus in the third embodiment of theinvention. In the embodiment, the radiation imaging apparatus in which aplurality of reading out circuit units 108 are provided and onecapacitor element 301 and one correction channel connected to thecapacitor element 301 are arranged for each reading out circuit unit 108will be described.

An example in which one set of the capacitor element 301 and thecorrection channel are arranged for one reading out circuit unit 108 isillustrated in FIG. 10 for convenience of description. However, in theembodiment, the number of sets of the capacitor elements 301 and thecorrection channels is not limited to the number as illustrated in FIG.10 but, for example, ten sets of the capacitor elements 301 and thecorrection channels may be provided for each of the eleven reading outcircuit units 108.

A case where there are a plurality of reading out circuit units 108 asmentioned above and one A/D converter 210 receives outputs of aplurality of reading out circuit units 108 will be described. In thiscase, a switch whose enabling state is controlled by the control signalCS is provided between the reading out circuit units 108 and the A/Dconverter 210, thereby allowing the outputs from the reading out circuitunits 108 to be switched. The buffer amplifier 209 is provided in eachreading out circuit unit 108. Other driving methods, functions, and thelike are similar to those in the first embodiment and FIG. 1.

FIG. 11 is a conceptual diagram illustrating a correcting method of aline noise in the third embodiment of the invention. According to theline noise correcting method in the third embodiment, correction dataI(m, 3) and I(m, 6) obtained from the two correction channelscorresponding to the two reading out circuit units 108 for the sameperiod of time as that of the reading operation of each row of thesensor array are averaged. After that, a subtracting process of theX-ray image data I(m, n) and the averaged correction data is executed.That is, a correction unit 1301 calculates the following equation inorder to obtain the corrected X-ray image data I′(m, n):

I′(m, n)=I(m, n)−(I(m, 3)+I(m, 6))/(2×p)

If there are three or more correction data, a plurality of correctiondata obtained for the same period of time are averaged, a subtractingprocess of the averaged correction data and the X-ray image dataobtained for the same period of time is executed and the correctingprocess of the line noise is executed.

In the embodiment, by using the mean value of a plurality of correctiondata I(m, 3) and I(m, 6), a contribution degree of the random noisecomponent which is generated in the capacitor elements 301 andcorrection channels connected thereto can be further reduced at the timeof the correcting process in a manner similar to the second embodiment.Thus, the line noise can be corrected more accurately. The above randomnoise component includes the 1/f noise of the operation amplifier 205and the variable gain amplifier unit 204 of the correction channel andthe KTC noise of the transfer switch or the like used in the correctionchannel of the S/H circuit unit 207.

A structure of the radiation imaging apparatus in the third embodimentof the invention will be described with reference to FIG. 12. FIG. 12 isa schematic diagram typically illustrating a structure of the radiationimaging apparatus in the third embodiment of the invention. A printedwiring board 1501 for reading out is provided. The reading out circuitunits 108 are mounted on a TCP (Tape Carrier Package) 1502 for readingout formed by a flexible printed wiring board. Wirings 1503 and 1504 areconnected to the capacitor elements 301. The wirings 1503 and 1504 arealso first conductive layers each serving as one electrode of thecapacitor element 301. A second conductive layer 1505 functions as theother electrode of the capacitor element 301 and a wiring connected tothe other electrode. The pixel region 211 of the sensor array isprovided on an insulating substrate 1506 such as a glass substrate. Aprinted wiring board 1507 for driving is provided. The driving circuitunits 112 are mounted on a TCP 1508 for driving formed from a flexibleprinted wiring board. An area sensor of the radiation imaging apparatusis formed by a method whereby an IC chip of the reading out circuitunits 108 and the driving circuit units 112 formed by the monosiliconprocess is mounted onto the TCP and the TCP is connected to the sensorarray formed by a plurality of pixels, signal wirings, driving wirings,and bias wiring. Further, the TCPs 1502 and 1508 are electricallyconnected to the printed wiring boards 1501 and 1507 for applyingvarious power source voltages to the reading out circuit units 108 andthe driving circuit units 112 and transmitting and receiving signalsthereto/therefrom, respectively.

The capacitor element 301 in the embodiment is formed on the insulatingsubstrate 1506 outside of the pixel region 211 (outer periphery of thepixel region 211) of the sensor array surrounded by a circle shown by abroken line in FIG. 12. In the construction illustrated in FIG. 12, fourcapacitor elements 301 are provided for each reading out circuit unit108.

A structure of the capacitor element 301 is illustrated in a regionsurrounded by a circle in FIG. 12. The capacitor element 301 isconstructed by: the first conductive layers 1503 and 1504 each servingas one electrode of the capacitor element 301; the other electrode ofthe capacitor element 301 and the second conductive layer 1505 servingas a wiring connected to the other electrode; and an insulating layer(not shown) such as an amorphous silicon nitride film arranged betweenthem.

One of the two electrodes 1503/1504 and 1505 of the capacitor element301 is connected to a second operation amplifier in the reading outcircuit unit 108. The other electrode is led out to the outside of thepixel region 211 of the sensor array through the TCP and is electricallyconnected to the sensor power source or the reference power source ofthe operation amplifier on the printed wiring board.

Although the four reading out circuit units 108 and the four drivingcircuit units 112 are provided in the embodiment, the number of readingout circuit units 108 and the number of driving circuit units 112 arenot limited to 4 but a necessary number of reading out circuit units 108and driving circuit units 112 may be properly provided according to thenumber of pixels of the sensor array or an area of the pixel region 211.

Fourth Embodiment

An image processing method using a radiation imaging apparatus in thefourth embodiment of the invention will now be described with referenceto FIG. 13. FIG. 13 is a conceptual diagram for describing a correctingmethod using the radiation imaging apparatus in the fourth embodiment ofthe invention. In the embodiment, in addition to the obtainment of theX-ray image described in one of the first to third embodiments, data ofan offset image is obtained and a correction is made by using the offsetimage data. The correction using the offset image data denotes a processfor correcting an X-ray image by using an image which includes a noisecomponent such as FPN (Fixed Pattern Noise) and the like and which hasbeen fetched without irradiating the X-ray. A point that the fourthembodiment differs from the first embodiment will be describedhereinbelow.

Since the offset image is an image in which the signals of the pixelshave been fetched without irradiating the X-ray as mentioned above, itis an image in which a dark current of the pixel, an output of thedefective pixel, an electric offset component, and the like aredominant. By subtracting the offset image from the X-ray image, the darkcurrent of the pixel, the output of the defective pixel, and theelectric offset component which exist in the X-ray image are removed, sothat picture quality can be improved.

However, since the line noise is also multiplexed to the offset imageitself, if the correcting process is executed by the offset imagecontaining the line noise, an influence of the line noise of the offsetimage is exerted on the X-ray image. In the embodiment, therefore, inaddition to the correction in the first embodiment, after the line noisewhich is multiplexed to the offset image is further corrected, theoffset of the X-ray image is corrected, so that the multiplex of theline noise can be suppressed.

The data of the X-ray image and the data of the offset image obtainedfrom the sensor array are written in the frame memory. As schematicallyillustrated in FIG. 13, a correction unit 1403 makes a correction bycorrecting data I(m, n) of each offset image by the correction data I(m,4) from the capacitor element 301 obtained simultaneously with theoffset image data. That is, in a manner similar to the first embodiment,the correction unit 1403 calculates the following equation in order toobtain corrected offset image data I′(m, n):

I′(m, n)=I(m, n)−I(m, 4)/p

The processing of the X-ray image data and the operation of thecorrection unit 1402 are omitted because their details have beendescribed in the first embodiment. A switch 1401 switches the processesof the X-ray image and the offset image.

A subtracting unit 1404 executes a subtracting process of the correctedX-ray image data and the corrected offset image data obtained asmentioned above and outputs the offset corrected X-ray image data.

A radiographing method in which the offset correction is made as shownin the embodiment can be embodied in any one of the first to thirdembodiments. Although the two correction units 1402 and 1403 for theX-ray image and the offset image are prepared in FIG. 13, they areillustrated in the diagram for convenience of description. If the timingfor obtaining the X-ray image and the timing for obtaining the offsetimage are deviated, the line noise correcting processes of those twoimages can be executed by one correction unit. In the embodiment, theoffset image may be obtained just after completion of the X-rayradiographing or can be also previously obtained before the X-rayradiographing. In a manner similar to the first embodiment, thecorrection units 1402 and 1403 and the subtracting unit 1404 can berealized by a method whereby the control PC 103 executes a program.

According to the invention, the line noise included in the obtainedX-ray image is obtained simultaneously with the obtainment of the imageby an element for correction prepared separately from the sensor arraywhich is used to obtain the image and by a reading out circuit connectedto such a correction element. By correcting the X-ray image by the datahaving the line noise component, the line noise in the image can beproperly removed.

Since the capacitor element is used as a correction element, unlike thecase of using a dark output of the pixel, an influence by a noise due toa dark current of the pixel or an influence by a fixed pattern noise dueto a thermal noise, a lattice defect, or the like is reduced.

By setting a capacitance of the capacitor element as a correctionelement to a value which is larger than, desirably, a value which isinteger times as large as a capacitance of the signal wiring,sensitivity of the line noise can be raised. In such a case, bymultiplying the line noise data detected at the time of the correctingprocess by a coefficient p as a ratio between the signal wiringcapacitance and the capacitance of the correction element, the linenoise can be properly corrected.

According to the method as mentioned above, by the subtracting process,a degree at the time when the random noise component generated in thereading out circuit unit is multiplexed as a line noise is suppressedand the line noise can be more effectively removed.

As a second reading out circuit and a correction element, since thesecond reading out circuits and correction elements of the numbers asmany as the number of signal wirings are not always necessary, they canbe easily mounted. Since there is no need to change the structure of thepixel region 211 of the sensor array, there is such an advantage thatthe characteristics of the sensor array are not sacrificed.

In each of the above embodiments, only a specific example for embodyingthe invention has been shown. A technical scope of the invention shouldnot be limitatively interpreted by those examples. That is, theinvention can be embodied by various forms without departing from itstechnical idea or its principal feature.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. A radiation imaging apparatus comprising: a conversion unit having apixel region in which a plurality of pixels are arranged in a matrix,wherein the pixel includes a conversion element converting radiationinto an electric charge and a switch element outputting an electricsignal based on the electric charge; a capacitor element arrangedoutside of the pixel region; a reading out circuit unit for reading outthe electric signals from the pixels row by row, wherein the reading outcircuit unit reads out, in parallel, a signal from the capacitor elementand the electric signal from the pixel; and a correction unit forcorrecting the electric signal based on the signal from the capacitorelement.
 2. The radiation imaging apparatus according to claim 1,wherein the reading out circuit unit reads out, in parallel, the signalfrom the capacitor element and the electric signals from the pixels of apredetermined row, and also reads out, in parallel, the signal from thecapacitor element and the electric signals from the pixels of the otherrow different from the predetermined row. 3-4. (canceled)
 5. Theradiation imaging apparatus according to claim 1, wherein the conversionunit has a wavelength converter for converting a radiation into light,and a photoelectric conversion element for converting the light into theelectric charge.
 6. The radiation imaging apparatus according to claim1, wherein the switching element is a thin film transistor formed on aninsulating substrate.
 7. (canceled)
 8. A computer-readable recordingmedium storing a readable program for operating a computer to execute acontrolling method of a radiation imaging apparatus comprising: aconversion unit having a pixel region in which a plurality of pixels arearranged in a matrix, wherein the pixel includes a conversion elementconverting radiation into an electric charge and a switch elementoutputting an electric signal based on the electric charge; a capacitorelement arranged outside of the pixel region; and a reading out circuitunit for reading out the electric signals from the pixels row by row,wherein the program operates the computer to execute steps of: readingout by the reading out circuit unit, in parallel, a signal from thecapacitor element and the electric signal from the pixel; and correctingthe electric signal based on the signal from the capacitor element. 9.The radiation imaging apparatus according to claim 1, wherein theswitching element is a thin film transistor formed on an insulatingsubstrate.
 10. A controlling method of a radiation imaging apparatuscomprising: a conversion unit having a pixel region in which a pluralityof pixels are arranged in a matrix, wherein the pixel includes aconversion element converting radiation into an electric charge and aswitch element outputting an electric signal based on the electriccharge; a capacitor element arranged outside of the pixel region; and areading out circuit unit for reading out the electric signals from thepixels row by row, wherein the method comprises steps of: reading out bythe reading out circuit unit, in parallel, a signal from the capacitorelement and the electric signal from the pixel; and correcting theelectric signal based on the signal from the capacitor element.
 11. Acomputer-readable recording medium storing a readable program foroperating a computer to execute a controlling method of a radiationimaging apparatus comprising: a conversion unit having a pixel region inwhich a plurality of pixels are arranged in a matrix, wherein the pixelincludes a conversion element converting radiation into an electriccharge and a switch element outputting an electric signal based on theelectric charge; a capacitor element arranged outside of the pixelregion; and a reading out circuit unit for reading out the electricsignals from the pixels row by row, wherein the program operates thecomputer to execute steps of: reading out by the reading out circuitunit, in parallel, a signal from the capacitor element and the electricsignal from the pixel; and correcting the electric signal based on thesignal from the capacitor element.